What is wrong with the naming of this file?

public class exercise$01\_02\{$

public static void main$($String$[]$ args$)\{$

$//$Display message Welcome to Java five times on the console

System.out.println$("$Welcome to Java"$)$;

System.out.println$("$Welcome to Java"$)$;

System.out.println$("$Welcome to Java"$)$;

System.out.println$("$Welcome to Java"$)$;

System.out.println$("$Welcome to Java"$)$;

$\}$

$\}$